Avalanche Forecast

Archived

Jan 18th, 2021–Jan 19th, 2021

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

South Coast Inland.

Variable wind has made wind slab avalanches possible at upper elevations, especially in northern parts of the region.

Confidence

Moderate - Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

MONDAY NIGHT: Clear skies, moderate ridgetop wind from the north, treeline temperatures drop to -8 C.

TUESDAY: Clear skies in the morning then increasing cloud in the afternoon, southwest ridgetop wind building to strong, treeline temperatures around -5 C with freezing level around 1000 m.

WEDNESDAY: A trace of snow overnight then mix of sun and cloud during the day, light west wind, treeline temperatures around -6 C.

THURSDAY: Mostly cloudy, light southwest wind, treeline temperatures around -6 C.

Avalanche Summary

Over the weekend a few natural wind slab avalanches and cornice falls were reported in the northern parts of the region (up to size 2).

A widespread natural avalanche cycle size 2-3 occurred throughout the region during a storm last week. Avalanche character was predominantly storm slab in the snowy north of the region and wet loose or glide slab in the rainy south. Northwest of Pemberton, several stepped down to buried weak layers resulting in very large (size 3-4) persistent slab avalanches.

Snowpack Summary

In the south of the region, fluctuating freezing levels during the last storm have resulted in a crust to ridgecrest. At upper elevations, 5-10 cm of dry snow has been blown around by the wind, exposing the crust in some areas and building wind slabs on top of it in others. The lower snowpack is well settled.

In the north, upper elevations are extensively wind affected. A widespread surface crust exists below 1600 m. A melt-freeze crust from early December is found around 200 cm deep in the snowpack. This crust may have sugary faceted grains sitting above it. This persistent weak layer is most prevalent northwest of Pemberton where large avalanches have failed on this interface recently.

Terrain and Travel

Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
Pay attention to cornices and give them a wide berth when traveling on or below ridges.
Conditions may have improved, but be mindful that deep instabilities are still present.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.